java中常见对象——StringBuffer

Demo:

public class StringBufferDemo {

public static void main(String[] args) {

// public StringBuffer():无参构造方法

StringBuffer sb = new StringBuffer();

System.out.println("sb:" + sb);

System.out.println("sb.capacity():" + sb.capacity());

System.out.println("sb.length():" + sb.length());

System.out.println("--------------------------");

// public StringBuffer(int capacity):指定容量的字符串缓冲区对象

StringBuffer sb2 = new StringBuffer(50);

System.out.println("sb2:" + sb2);

System.out.println("sb2.capacity():" + sb2.capacity());

System.out.println("sb2.length():" + sb2.length());

System.out.println("--------------------------");

// public StringBuffer(String str):指定字符串内容的字符串缓冲区对象

StringBuffer sb3 = new StringBuffer("hello");

System.out.println("sb3:" + sb3);

System.out.println("sb3.capacity():" + sb3.capacity());

System.out.println("sb3.length():" + sb3.length());

}

}

Demo:

public class StringBufferDemo {

public static void main(String[] args) {

// 创建字符串缓冲区对象

StringBuffer sb = new StringBuffer();

// public StringBuffer append(String str)

// StringBuffer sb2 = sb.append("hello");

// System.out.println("sb:" + sb);

// System.out.println("sb2:" + sb2);

// System.out.println(sb == sb2); // true

// 一步一步的添加数据

// sb.append("hello");

// sb.append(true);

// sb.append(12);

// sb.append(34.56);

// 链式编程

sb.append("hello").append(true).append(12).append(34.56);

System.out.println("sb:" + sb);

// public StringBuffer insert(int offset,String

// str):在指定位置把任意类型的数据插入到字符串缓冲区里面,并返回字符串缓冲区本身

sb.insert(5, "world");

System.out.println("sb:" + sb);

}

}

Demo:

public class StringBufferDemo {

public static void main(String[] args) {

// 创建对象

StringBuffer sb = new StringBuffer();

// 添加功能

sb.append("hello").append("world").append("java");

System.out.println("sb:" + sb);

// public StringBuffer deleteCharAt(int index):删除指定位置的字符，并返回本身

// 需求：我要删除e这个字符，肿么办?

// sb.deleteCharAt(1);

// 需求:我要删除第一个l这个字符，肿么办?

// sb.deleteCharAt(1);

// public StringBuffer delete(int start,int

// end):删除从指定位置开始指定位置结束的内容，并返回本身

// 需求：我要删除world这个字符串，肿么办?

// sb.delete(5, 10);

// 需求:我要删除所有的数据

sb.delete(0, sb.length());

System.out.println("sb:" + sb);

}

}

Demo:

public class StringBufferDemo {

public static void main(String[] args) {

// 创建字符串缓冲区对象

StringBuffer sb = new StringBuffer();

// 添加数据

sb.append("hello");

sb.append("world");

sb.append("java");

System.out.println("sb:" + sb);

// public StringBuffer replace(int start,int end,String

// str):从start开始到end用str替换

// 需求：我要把world这个数据替换为"节日快乐"

sb.replace(5, 10, "节日快乐");

System.out.println("sb:" + sb);

}

}

Demo:

public class StringBufferDemo {

public static void main(String[] args) {

// 创建字符串缓冲区对象

StringBuffer sb = new StringBuffer();

// 添加数据

sb.append("霞青林爱我");

System.out.println("sb:" + sb);

// public StringBuffer reverse()

sb.reverse();

System.out.println("sb:" + sb);

}

}

Demo:

public class StringBufferDemo {

public static void main(String[] args) {

// 创建字符串缓冲区对象

StringBuffer sb = new StringBuffer();

// 添加元素

sb.append("hello").append("world").append("java");

System.out.println("sb:" + sb);

// 截取功能

// public String substring(int start)

String s = sb.substring(5);

System.out.println("s:" + s);

System.out.println("sb:" + sb);

// public String substring(int start,int end)

String ss = sb.substring(5, 10);

System.out.println("ss:" + ss);

System.out.println("sb:" + sb);

}

}

Demo:

public class StringBufferTest {

public static void main(String[] args) {

// String -- StringBuffer

String s = "hello";

// 注意：不能把字符串的值直接赋值给StringBuffer

// StringBuffer sb = "hello";

// StringBuffer sb = s;

// 方式1:通过构造方法

StringBuffer sb = new StringBuffer(s);

// 方式2：通过append()方法

StringBuffer sb2 = new StringBuffer();

sb2.append(s);

System.out.println("sb:" + sb);

System.out.println("sb2:" + sb2);

System.out.println("---------------");

// StringBuffer -- String

StringBuffer buffer = new StringBuffer("java");

// String(StringBuffer buffer)

// 方式1:通过构造方法

String str = new String(buffer);

// 方式2：通过toString()方法

String str2 = buffer.toString();

System.out.println("str:" + str);

System.out.println("str2:" + str2);

}

}

Demo:

public class StringBufferTest2 {

public static void main(String[] args) {

// 定义一个数组

int[] arr = { 44, 33, 55, 11, 22 };

// 定义功能

// 方式1：用String做拼接的方式

String s1 = arrayToString(arr);

System.out.println("s1:" + s1);

// 方式2:用StringBuffer做拼接的方式

String s2 = arrayToString2(arr);

System.out.println("s2:" + s2);

}

// 用StringBuffer做拼接的方式

public static String arrayToString2(int[] arr) {

StringBuffer sb = new StringBuffer();

sb.append("[");

for (int x = 0; x < arr.length; x++) {

if (x == arr.length - 1) {

sb.append(arr[x]);

} else {

sb.append(arr[x]).append(", ");

}

}

sb.append("]");

return sb.toString();

}

// 用String做拼接的方式

public static String arrayToString(int[] arr) {

String s = "";

s += "[";

for (int x = 0; x < arr.length; x++) {

if (x == arr.length - 1) {

s += arr[x];

} else {

s += arr[x];

s += ", ";

}

}

s += "]";

return s;

}

}

Demo:

public class StringBufferTest3 {

public static void main(String[] args) {

// 键盘录入数据

Scanner sc = new Scanner(System.in);

System.out.println("请输入数据：");

String s = sc.nextLine();

// 方式1：用String做拼接

String s1 = myReverse(s);

System.out.println("s1:" + s1);

// 方式2：用StringBuffer的reverse()功能

String s2 = myReverse2(s);

System.out.println("s2:" + s2);

}

// 用StringBuffer的reverse()功能

public static String myReverse2(String s) {

// StringBuffer sb = new StringBuffer();

// sb.append(s);

// StringBuffer sb = new StringBuffer(s);

// sb.reverse();

// return sb.toString();

// 简易版

return new StringBuffer(s).reverse().toString();

}

// 用String做拼接

public static String myReverse(String s) {

String result = "";

char[] chs = s.toCharArray();

for (int x = chs.length - 1; x >= 0; x--) {

// char ch = chs[x];

// result += ch;

result += chs[x];

}

return result;

}

}

Demo:

public class StringBufferTest4 {

public static void main(String[] args) {

// 创建键盘录入对象

Scanner sc = new Scanner(System.in);

System.out.println("请输入一个字符串：");

String s = sc.nextLine();

// 一个一个的比较

boolean b = isSame(s);

System.out.println("b:" + b);

//用字符串缓冲区的反转功能

boolean b2 = isSame2(s);

System.out.println("b2:"+b2);

}

public static boolean isSame2(String s) {

return new StringBuffer(s).reverse().toString().equals(s);

}

// public static boolean isSame(String s) {

// // 把字符串转成字符数组

// char[] chs = s.toCharArray();

//

// for (int start = 0, end = chs.length - 1; start <= end; start++, end--) {

// if (chs[start] != chs[end]) {

// return false;

// }

// }

//

// return true;

// }

public static boolean isSame(String s) {

boolean flag = true;

// 把字符串转成字符数组

char[] chs = s.toCharArray();

for (int start = 0, end = chs.length - 1; start <= end; start++, end--) {

if (chs[start] != chs[end]) {

flag = false;

break;

}

}

return flag;

}

}

demo：

public class StringBufferDemo {

public static void main(String[] args) {

String s1 = "hello";

String s2 = "world";

System.out.println(s1 + "---" + s2);// hello---world

change(s1, s2);

System.out.println(s1 + "---" + s2);// hello---world

StringBuffer sb1 = new StringBuffer("hello");

StringBuffer sb2 = new StringBuffer("world");

System.out.println(sb1 + "---" + sb2);// hello---world

change(sb1, sb2);

System.out.println(sb1 + "---" + sb2);// hello---worldworld

}

public static void change(StringBuffer sb1, StringBuffer sb2) {

sb1 = sb2;

sb2.append(sb1);

}

public static void change(String s1, String s2) {

s1 = s2;

s2 = s1 + s2;

}

}